Recently, high-efficiency induction motors are used in view of the increasing demand for energy-saving. In order to improve the efficiency of this motor, a laminate thickness of a core is increased or a filling rate of winding wires is improved. In addition, as a material for the electrical steel sheet used in the core is promoted an exchange from the conventional low-grade material to a high-grade material having a lower iron loss.
A steel sheet used as a core material of the induction motor is required to be not only low in the iron loss but also low in the effective excitation current at a predetermined magnetic flux density from a viewpoint of reducing the copper loss. In order to reduce the excitation current, it is effective to increase a magnetic flux density of the core material.
Further, in a driving motor used in hybrid cars and electric cars which become popular rapidly, it is necessary to have a high torque at startup or accelerated period, so that it is desired to further improve a magnetic flux density.
As an electrical steel sheet having a high magnetic flux density, for example, Patent Document 1 discloses a non-oriented electrical steel sheet in which 0.1-5 mass % of Co is added to a steel having Si≤4 mass %.